Silicone oils, and especially fluorosilicone oils, of low viscosity have found utility in a variety of applications including antifoams and as a base oil for non-curing sealants and greases. These oils have been made in the past by the acidic catalyzed polymerization of the silicone, e.g., fluorosilicone, cyclic siloxane trimer. The cyclic trimer, however, is more difficult and expensive to prepare than the corresponding cyclic tetramer, but prior references, e.g., Pierce et al., U.S. Pat. No. 2,979,519, have asserted that such cyclic tetramers could not be polymerized. In addition, the use of acidic catalysts for preparing the oils has a serious limitation. Many useful silicone oils have small quantities of vinyl groups for use in vinyl to silicone hydride cures. The acidic catalysts can react with the vinyl groups and cause contamination of the oil.
Diorganopolysiloxane gums having a viscosity that varies from 10,000 to 200,000,000 centipoise viscosity at 25.degree.C., have been produced for use as the basic ingredient in heat vulcanizable silicone rubber compositions, utilizing as starting materials, cyclicsiloxanes. The usual procedure is to begin with diorganochlorosilanes of high purity, to hydrolyze such diorganochlorosilanes in water at about room temperature, to recover the hydrolyzate and to separate the water from it, and then to add to the hydrolyzate a catalyst, such as potassium hydroxide. The resulting mixture is heated at elevated temperatures of above 100.degree.C. for a period of time about 1 hour to 8 hours and distilling overhead leads to a large proportion of cyclic trisiloxanes, cyclic tetrasiloxanes, cyclic pentasiloxanes and the like. It is easiest to recover the cyclic tetramers from such hydrolyzate cracking mixtures.
If the sole substituent groups are methyl, vinyl or phenyl groups, such cyclic tetrasiloxanes may then be equilibrated in the presence of a catalyst, such as potassium hydroxide. Also included are chain-stoppers, e.g., disiloxanes and/or low molecular weight diorganopolysiloxanes containing triorganosiloxy terminal groups have a chain-stopping function. After methyl-substituted cyclic tetrasiloxanes are equilibrated with small amounts of potassium hydroxide at temperatures of above 150.degree.C., there results an equilibrium mixture wherein about 85 percent of the cyclic tetrapolysiloxanes are converted into the diorganopolysiloxane gum.
At equilibrium, as much of the tetrasiloxanes is being formed into the diorganopolysiloxane gum as is the diorganopolysiloxane gum breaking down and reforming cyclic siloxanes. With methyl substitution, at most only 85 percent of the original cyclic tetrasiloxanes can be converted to the desired diorganopolysiloxane gum and the other 15% by weight of the mixtures is cyclic siloxane.
At equilibrium, the catalyst is neutralized and the volatiles (including cyclics) are removed to leave desired diorganopolysiloxane gum, having a viscosity, e.g., of from 1,000 to 200,000,000 centipoise viscosity at 25.degree.C.
In distinct contrast, however, when attempts are made to form diorganopolysiloxanes wherein at least one of the organo groups attached to the silicon atom is an aliphatic radical or halogenated aliphatic radical of three carbon atoms or more, it is found that tetracyclic siloxanes and higher cyclic siloxanes, such as pentacyclic siloxanes and hexacyclic siloxanes will not be useful in an equilibration procedure such as that described above. Specifically, if such cyclic tetrasiloxanes contain at least one organo substituent group on the silicon atom which is aliphatic or haloaliphatic of three carbon atoms or more, then at the equilibration point, there will be a very low, commercially unsuccessful yield of diorganopolysiloxane gum. Illustratively, only 10 to 20 percent of the cyclic tetrasiloxane or higher cyclic siloxane can be converted to the diorganopolysiloxane gum, as contrasted to the 85% by weight yield which is easily obtained with octamethyltetrasiloxanes.
The state of the art is shown, for example, in Pierce et al., U.S. Pat. No. 2,979,519, which is incorporated by reference. It is taught therein that commercially successful rubbers cannot be prepared by known methods from cyclic siloxanes of the formula, ##STR1## where x is 4 or more, e.g., the tetramers, pentamers, etc. In the publically available file of the Pierce et al patent, it is disclosed moreover that diorganopolysiloxane gums of high molecular weight cannot be formed from cyclic tetrasiloxanes where one of the substituent groups in the cyclic polysiloxane contains 3 carbon atoms or more and, specifically, one which contains a radical in which R is perfluoroalkyl. U.S. Pat. No. 2,979,519, and its publically available file, teach that although high molecular weight diorganopolysiloxane gums are not formed by known methods from such tetrasiloxanes, they can readily be formed from the corresponding cyclic trisiloxanes.
If low molecular weight polysiloxane oils having a low viscosity and having at least one substituent group comprising alkyl or haloalkyl of at least 3 carbon atoms are desired, it has been found that such oils also are formed from cyclic tetrasiloxanes by known methods only in low yields, such as 10 to 15 percent. Moreover, after analysis the product is found to be predominately composed of cyclics rather than the desired low viscosity desired polymers at termination.
A further difficulty in using the process of Pierce et al to form low molecular weight polysiloxane oils even from cyclic trisiloxanes is that such cyclic trisiloxanes immediately react to form high molecular weight polymers under the stated conditions. Thus, even if there is used an exceptionally large amount of chain-stopper in the reaction mixture, the reaction of U.S. Pat. No. 2,979,519 cannot be controlled to form low molecular weight polymers.
A further difficulty with the Pierce et al procedure is that the cyclic trisiloxanes, which are required, are formed only in low yield during the initial cracking of the hydrolyzate with potassium hydroxide. The cyclic tetrasiloxane is formed in greater amounts. This requires the utilization of an energy-inefficient high reflux distillation procedure to maximize the yield of cyclic trisiloxanes from the cracking process. This means that even though the cyclic trisiloxanes have tended to react more readily by known procedures, overall, the process for forming polymers from cyclic trisiloxanes is still more expensive than it would have been if a successful method is provided for using cyclic tetrasiloxanes.
It has now been unexpectedly found that at certain low temperature ranges, which have not been envisioned previously, and in the presence of certain selected catalysts, cyclic tetrasiloxanes wherein at least one of the organo substituent groups appended to the silicon atom is an aliphatic or haloaliphatic radical of 3 carbon atoms or more, such as --CH.sub.2 CH.sub.2 R.sup.5 R.sup.5 being, e.g., a perfluoroalkyl radical, can be readily equilibrated in high yields. The cyclic tetrasiloxanes can be equilibrated to produce either low molecular weight oils, or high molecular weight diorganopolysiloxane gums, the latter suitable for forming heat vulcanizable silicone rubber compositions. This application is primarily concerned with the production of oils.
It is, accordingly, a principal object of the present invention to provide for a process for producing low molecular weight diorganopolysiloxane oils in high yield wherein one of the organo groups attached to the silicon atom is an aliphatic or haloaliphatic radical of at least 3 carbon atoms or more.
It is an object of this invention to provide a means for producing low molecular weight diorganopolysiloxane oils, in which one of the organo groups attached to the silicon atom is an aliphatic or haloaliphatic radical of 3 carbon atoms or more from a cyclic tetrasiloxane and/or mixtures of cyclic tetrasiloxanes containing such groups.
Still another object of the present invention is to provide a process for producing low molecular weight diorganopolysiloxane oils having a viscosity from 50 to 100,000 centipoise at 25.degree.C., wherein at least one of the organo groups attached to the silicon atoms is an aliphatic or haloaliphatic radical of 3 carbon atoms or more, by equilibrating cyclic tetrasiloxanes and mixtures of cyclic tetrasiloxanes at relatively low temperatures in the presence of selected catalysts.
An additional object of the present invention is to provide a process for producing diorganopolysiloxane oils having a viscosity from 50 to 100,000 centipoise at 25.degree.C., wherein at least one of the organo groups attached to the silicon atoms is --CH.sub.2 CH.sub.2 R.sup.5, and wherein R.sup.5 is perfluoroalkyl, using cyclic tetrasiloxanes as starting materials.
A further object is to produce uncontaminated vinyl containing fluorosilicone oils by polymerizing a fluorosilicone cyclic tetramer with a non-acidic catalyst which is incapable of reacting with any vinyl groups.